Accelerator return springs are well known in automotive internal combustion engine applications for biasing a throttle valve to a predetermined position, typically a closed or idle position. The return springs, which can be either single or dual wound, are usually a coil-type tension spring attached to a throttle cam on one end and to the engine block on the other.
During engine operations, the internal combustion cycle produces vibrations which may excite the natural frequency of the return spring. When that occurs, the vibrational energy in the spring may be transferred through the accelerator cable to the accelerator pedal resulting in a phenomenon known as "pedal buzz". Pedal buzz can annoy a vehicle driver and thus poses a concern for automotive engineers and designers.
One approach to the problem is to enclose the return spring 102 with an external damper 104, such as that shown in FIG. 8. An external damper, however, typically does not fit tightly to the spring for adequate damping. In addition, the external damper may vibrate at its own natural frequency, potentially compounding the pedal buzz problem.
Another approach adds mass to the return spring assembly to shift the natural frequency beyond the range normally encountered during engine operation. Increased mass, however, has the disadvantages of decreasing fuel economy and increasing component cost.